Losses in IGBTs or FWDs mounted on inverters or converters have been reduced year after year. Accordingly, current densities of chips have been improved and chip sizes have been reduced. In recent years, however, losses in IGBTs or FWDs are approaching a limit value, and development of power devices using SiC as a raw material and development of RC-IGBT having both of IGBT and FWD performance or the like are also underway.
Power devices using SiC as the raw material can be used at high temperatures and are also expected to be able to drastically reduce losses. However, power devices using SiC have problems like high prices of SiC wafer materials and faults caused by defects in SiC, and it is therefore estimated that it will take some time until the power devices using SiC are widely spread in the market.
In contrast, RC-IGBTs can be implemented by combining IGBTs and FWDs using Si as the raw material whose development has been advanced so far. If structures of an IGBT region and an FWD region can be optimized, it is possible to manufacture an RC-IGBT with stable yield using a current manufacturing apparatus. However, it is extremely difficult to simultaneously optimize the structures of the IGBT region and the FWD region and make their respective losses equivalent to losses of individually manufactured IGBT anti FWD.
In a normal FWD, a technique for shortening its lifetime in Si through Pt diffusion and irradiation of electron beams is adopted to reduce recovery losses. However, the RC-IGBT has a problem that if its lifetime in Si is shortened, a total loss of the IUBT (sign of on-time losses and switching losses) is increased.
In order to reduce recovery losses without shortening the lifetime in Si, it is effective to suppress injection of holes from the anode region when the FWD is forward-biased and energized. For that purpose, the concentration of the anode region is lowered. However, since holes are injected also from the P-type diffusion layer on the chip surface other than the anode region, attention needs to be paid to the design of the P-type diffusion layer other than the anode region.
In order to reduce recovery losses in, for example, the RC-IGBT, a technique is being proposed which forms no reverse side n+ region which becomes the cathode layer of the diode directly below the P-type base layer of the IGBT (e.g., see PTL 1).